Method and apparatus for processing a preform

ABSTRACT

The present invention relates to a method and an apparatus for processing a preform and/or drawing an optical fiber. The method is characterized by securing the preform ( 2 ) to the processing device by means of at least two separate gripping means ( 4, 6 ), heating the preform ( 2 ) or a section thereof by means of at least one heating device at least locally, generating a tension in the preform ( 2 ) by means of the gripping means ( 4, 6 ), and processing the preform ( 2 ) by moving one of the gripping means ( 4, 6 ) and the heating means ( 12 ) and keeping the gripping means ( 4, 6 ) on the side of the end product of the preform in position relative to the body of the processing device, whereby the end product produced also remains in position relative to the body of the processing device.

BACKGROUND OF THE INVENTION

The invention relates to a device according to the preamble of claim 1and to a method according to the preamble of claim 5 for processing apreform to alter its length and diameter, and to a device and methodaccording to claims 16 and 21 for drawing an optical fibre.

In the manufacture of an optical fibre, the blank, i.e. the preform, hasto be processed to obtain an outer diameter of the desired size, or tocorrect any form errors created in the preform, for instance variationsin the diameter and errors in the roundness or straightness of thepreform.

In the present context, a preform refers to a blank or a part thereof,from which the optical fibre is manufactured. The above parts couldinclude for example rods or tubes and different combinations thereof.The material of the preform could be for instance plastic, glass oranother corresponding material. The preform may also include severalconstituents. Processing a preform can involve stretching or forging ata constant or varying speed, during which the preform may also berotated at a constant or varying speed around its longitudinal axis.

From hereon, when referring to the stretching, drawing, forging or otherprocessing of a preform, the expression processing will be used, and, inthe same way, for the device used for the purpose, the expressionprocessing device, which comprises means for stretching, forging orother deformation of the preform, will be used.

In accordance with the prior art, a preform is processed in a processingdevice, wherein the preform is heated and subjected to a force in thedirection of its longitudinal axis. The processing of a preform isenabled by heating the preform with a heating device, e.g. a heatingfurnace, to make the preform soften in the heated section. At the sametime the processing device creates, tension, e.g. tensile stress, in thepreform, whereby the preform stretches in the heated and softenedsection. As the preform is stretched, its length increases and outerdiameter decreases, whereby a stretched preform of the desired thicknessis obtained from the processing device. The diameter of the preformobtained in the stretching can be adjusted as desired during the processfor a given purpose. In the same way, the preform can also be forged bysubjecting it to a compressive force, or its form can be altered in somecorresponding manner.

In accordance with the prior art, a preform processing device usuallycomprises two gripping means for securing the preform to the processingdevice, and one heating device for heating the preform to enable theprocessing thereof. The rod-like preform is usually secured at its endsto the gripping means, and during the processing process the preform issubjected to a force by moving at least one of the gripping means in theaxial direction of the preform away from or towards the other grippingmeans. Feeding the preform, tensioned by means of the gripping means,longitudinally through the heating device, enables processing of thepreform. Feeding the preform is implemented in accordance with the priorart by moving the preform through the heating device, fixedly installedin the processing device, by means of said two movable gripping means.This is implemented by moving both gripping means in the same direction,allowing the preform to be fed through the fixed, immobile heatingdevice. Another prior art manner of processing a preform is tomanufacture a processing device wherein only one of the gripping meansis movable relative to the body of the processing device, the otherbeing fixedly installed in the processing device. In accordance with theprior art, the movable gripping means is always at that end of thepreform from which the end product is produced as a result of stretchingor drawing. Herein, the gripping means at the opposite end of thepreform, the feed end, is arranged fixed. To enable processing of thepreform, the heating device is arranged movable relative to the body ofthe processing device, the preform being processed by moving one of thegripping means and the heating device.

In accordance with the prior art, a preform processing device comprisesthree modules; two gripping means for securing the preform to theprocessing device, and a heating device for heating the preform or asection thereof, two of which are arranged movable in theabove-described manner during the processing process.

Devices of the kind described above, comprising two movable modules, aredisclosed in U.S. Pat. No. 6,178,778, for example.

The basic principle in drawing an optical fibre is similar to that instretching a preform, but the drawing ratios in fibre drawing areconsiderably higher. The equipment for drawing a fibre also usuallycomprise two gripping means for securing the preform, from which thefibre is drawn, to a drawer, and at least one heating device for heatingthe preform to enable drawing of the fibre. Herein, fibre refers to aconventional solid optical fibre, hollow fibre, crystal fibre or anothercorresponding optical fibre made from plastic, glass or a correspondingproduction material for optical fibre.

The problem in the described prior art solution comprising two mobilemodules is that sufficiently stable conditions, wherein the oscillationsof the processing or drawing device are minimized thus eliminating theeffect of the oscillations on the quality of the end product, requiredin the processing, i.e. stretching, forging or another procedure forprocessing a preform or drawing a fibre, are almost impossible toachieve with the same processing device. This is essentially because inprior art solutions the end product is moved relative to the body of theprocessing device.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is thus to provide a method and an apparatusimplementing the method for solving the above problems and for enablingthe modification of the geometry of a preform as desired by reducing theoscillation directed to the end product by holding the end product,produced as the result of stretching or drawing, in position relative tothe body of the processing device and by enabling the selection of thedrawing or processing direction and easy installation of the preforminto the device. The object of the invention is achieved by a method anddevice that are characterized in what is stated in independent claims 1and 5, and 16 and 21. Preferred embodiments of the invention aredescribed in the dependent claims.

The object of the invention is achieved with a device for processing/stretching a preform or with a device for drawing a fibre, the devicecomprising at least two gripping means for securing the preform to theprocessing/ stretching device and at least one heating device forheating the preform or a section thereof to the desired temperature insuch a way that both the gripping means and the heating device arearranged movable, allowing all of them to be moved optionally by holdingthe end product produced in the stretching of the preform or the drawingof the fibre in position relative to the body of the processing device.The present invention is based on the device for processing the preformbeing manufactured such that all its modules, gripping means and heatingdevices are optionally separately movable. This allows the processing orstretching to be performed in the desired direction relative to the bodyof the processing device by holding the end product produced in theprocessing in position relative to the body of the processing device.

It is also preferable in the present invention that each of the grippingmeans and the heating device is independently movable and that the speedof movement and direction of movement of each of the gripping means andthe heating device are separately adjustable. It is also preferable thatthe gripping means for securing the preform to the processing devicealso comprise means for rotating the preform around its longitudinalaxis during the processing. The processing apparatus of the invention isexecutable as a vertical or horizontal structure or as a hybrid thereof.

The object of the present invention is achieved by a method ofprocessing a preform, the method utilizing the apparatus of theinvention by securing the preform to the processing device by means ofat least two separate gripping means, by heating the preform or asection thereof by means of at least one heating device at leastlocally, by generating a tension in the preform by means of the grippingmeans, and by processing the preform by feeding it to the heating deviceby moving one of the gripping means and the heating means in such amanner that the resulting end product is held in position with thesecond gripping means relative to the body of the processing device.

In the method, the speed of movement and direction of movement of thegripping means and the heating device, and the temperature of theheating device are preferably adjusted in such a manner that the preformis provided with a diameter of substantially the desired size as aresult of the processing. It is also preferable that the speed ofmovement and direction of movement of each gripping means and heatingdevice is adjusted separately. The preform can be rotated around itslongitudinal axis during the processing to improve the management of thesoftened preform and to correct the roundness of the preform.

An advantage of the method and device of the invention is that theposition in which the preform is installed and from which it is removedcan be selected more freely. At the same time, maintenance work on theapparatus becomes easier. Since the drawing can also be performed usingtwo movements, the third movement remains to be used for other processadjustment measures. When the preform is to be cut after the process,the point of cutting can also be selected more freely in the solution ofthe invention than in known solutions. In addition, holding the endproduct generated in the processing in position relative to the body ofthe processing device ensures the achievement of an end product havingthe best possible quality.

BRIEF DESCRIPTION OF THE FIGURES

In the following, preferred embodiments of the invention will bedescribed in detail with reference to the accompanying drawings, inwhich

FIG. 1 a shows the initial situation of the preform processing methodaccording to the present invention, the preform being installed in aprocessing device according to the present invention for stretching;

FIG. 1 b shows a situation in the preform processing method according tothe present invention, the preform being stretched with a processingdevice according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the present invention will be studied by means ofexemplary embodiments. These embodiments only act as examples of thedevice and method of the present invention, and do not restrict thescope of the invention; on the contrary, the embodiments of theinvention may vary within the scope of the claims.

Reference is made to FIG. 1 a showing an embodiment of a processingdevice according to the present invention. In this embodiment, saidprocessing device comprises a first gripping means 4 and a secondgripping means 6 for securing a preform to the processing device, aheating device 12 for heating the preform during the processing process,and rotation means 16 and 14 secured to the first and second grippingmeans 4 and 6, respectively, for rotating the preform around itslongitudinal axis. In accordance with FIG. 1 a, the elongated preform 2is installed in the processing device according to an embodiment of theinvention, a first end 10 of the preform being secured to the grippingmeans 4 and a second end 8 to the gripping means 6. FIG. 1 a shows theinitial situation in the preform processing method of the presentinvention, the preform being installed in a processing device accordingto the invention, whose gripping means 4 and 6 and heating device 12 aremovable at least in the longitudinal direction of the preform. In thisexemplary embodiment, the preform is stretched, but the method anddevice of the invention can also be used to forge the preform or subjectit to other processing procedures.

The device according to the present invention can also be provided withmore than two gripping means and/or cutting devices, all of which aremovable. In this case, some gripping means are secured between the endsof the preform. The processing device may also comprise severalindependently movable heating devices 12, allowing the preform to beheated at more than one point at the same time. This allows thestretching or forging to be performed in steps and different heatingtemperatures to be maintained in the heating devices 12. In addition,this would enable the processing to be started simultaneously at bothends of the preform or at different points of the preform.

In accordance with the present invention, the processing device isconfigured to enable separate control of each movable module 4, 6 and12, i.e. each module has independent drives, servo drives, for example.This allows each module 4, 6 and 12 to be moved at different speeds and,if needed, also in different directions, or held in position. The methodof the invention for processing a preform utilizes for instance theembodiment of the processing device of the invention of the typedescribed above in FIG. 1 The elongated preform 2 produced by the methodis secured to the processing device by means of the gripping means 4 and6. In the present exemplary embodiment of the method, the initialsituation is as shown in FIG. 1 a. The preform is first secured, andthen subjected to stretching.

In accordance with the present invention, the preform is stretched byutilizing the gripping means 4 and 6, both of which are movable, and themovable heating device 12. In the present embodiment, the stretching ofthe preform starts at its one end 8, and the stretching of the preformtakes place vertically from the top downwards. This means that theheating of the preform by means of the heating device 12 starts at oneend 8 of the preform, and at the same time, the preform is subjected totensile stress by moving the gripping means 4 and 6 relative to eachother. In the present embodiment, the lower gripping means 4 is moveddownwards in accordance with FIG. 1 b , and, as a result of thegenerated tensile stress, the stretching of the preform 2 starts at theupper end thereof, and the end product produced by the stretchingremains in position relative to the body of the stretcher. During theprocess, the heating device 12 glides downwards.

The preform 2, heated by means of the heating device 12, softens in thesection heated, whereby the tensile stress, generated in the preform bymeans of the gripping means 4 and 6, causes the stretching of thesoftened section of the preform 2. During the stretching, the diameterof the stretched section 3 of the preform is reduced.

FIG. 1 b shows the processing process by showing the relative movementsof the movable modules 4, 6 and 12 relative to each other, and thestretching of the preform 2. The rotation means 16 and 14 for rotatingthe preform during the processing process are secured to the grippingmeans 4 and 6 to allow them to move with the gripping means.

As the stretching of the preform 2 starts in the initial state inaccordance with FIG. 1 a , the preform 2 is heated at its upper end withthe heating device 12. Once the preform 2 is sufficiently heated, thepreform 2 is subjected to tensile stress by moving the lower grippingmeans 4 downwards in the longitudinal direction of the preform, and byholding the upper gripping means 6 in position. At the same time, theheating device 12 starts to be moved from the upper end 8 of the preform2 towards the lower end. The tensile stress generated by the movement ofthe gripping means 4 makes the heated preform stretch, and because theheating point of the preform, i.e. the stretching point, has tocontinuously move downwards along the preform 2 in the presentembodiment, the heating device 12 has to be moved downwards relative tothe movement of the lower end 10 of the preform 2.

In the previous exemplary embodiment, a stretched preform 3 is generatedfrom the upper end of the original non-stretched preform 2 as a resultof the processing process. The thickness of the generated stretchedpreform 3, i.e. the stretching ratio of the stretching process, ismanaged by means of the relative velocities of the movable modules andthe temperature of the heating device 12. The preform may also berotated around its longitudinal axis during the stretching process.Rotating the preform improves the management of the shape of the sectionthereof that softened as a result of the heating, and the stability ofthe processing process. In accordance with the invention, the endproduct generated as a result of the stretching remains in positionrelative to the body of the processing device, since the upper grippingmeans 6 are not moved during the stretching.

The above-described exemplary embodiment described stretching a preform,but a similar preform processing method and device, wherein both thegripping means and the heating device are movable, can also be used forforging a preform and in other preform processing processes.

Furthermore, a similar method can be utilized in drawing a fibre. Inthis case, the gripping means, located at that end of the preform fromwhich fibre is produced, are held in position relative to the body ofthe drawer. The immobile gripping means constitute or can comprise aspooler apparatus for coiling the produced fibre on a coil. Bothgripping devices can also be provided with a coiling apparatus enablingdrawing in the desired direction. The optical fibre thus generated iscoiled by means of the coiling device, attached to the gripping means,which is immobile relative to the body of the drawer, onto the coil suchthat both the furnace and the gripping means that moves relative to thebody of the drawer move relative to the receiving coiling device for theend product/optical fibre irrespective of the selected drawingdirection. In a preferred embodiment of the invention, the processingapparatus is configured to enable vertical stretching of the preform.All modules being movable allows the same apparatus to be used fordrawing from both the top downwards and from the bottom upwards,however, preferably from the top downwards, by simultaneously holdingthe end product generated as a result of the stretching/processing inposition relative to the body of the processing device. In addition, thepreform can be continuously rotated around its longitudinal axis toadjust the shape of the preform.

In the present invention, the preform can also be secured to theprocessing device with more than two gripping means, which may all beindependently movable or two or more can form a movable group, however,in such a manner that at least two gripping means or groups thereof areindependently movable. In addition, there may be several heating devicesinstalled such that one is able to move from the top downwards and thesecond from the bottom upwards, for example. The heating devices mayalso move in the same direction in succession, enabling stepwiseprocessing of the preform. The heating devices may move at the same or adifferent speed.

Such a structure according to the invention enables cutting the preform,implemented with a heat source at a freely selectable point, and, at thesame time, the installation and removal of the preform into and from theprocessing device are facilitated, as all modules are separatelycontrollable during the installation into and removal from thestretcher. Furthermore, stretching from the bottom upwards allows themelt section of the preform to be supported by the rigid, non-stretchedsection of the preform. This also enables the use of a higher heatingtemperature.

The above-described technology and device can also be utilized in MCVD,sleeving, and collapsing processes, in drawing and other correspondingoptical fibre production processes. Sleeving refers to the increase ofthe thickness of a solid or tubular preform by melting a tube of thesame or a different material onto an existing preform. Collapsing, inturn, refers to the collapsing of a tubular preform into a rod byremoving the free space on the inside of the tube by suction such thatthe inner walls of the tube melt together. The present inventionprovides the preform stretching process with a new kind of flexibilityand reduces the space required by the apparatus.

The present invention is not intended to be restricted to the aboveembodiments, but the gripping means, the heating devices and theirmobility, and the original shape and structure of the preform may varywithin the scope of the claims of the invention. It is essential in theinvention that, as distinct from the prior art, all modules of thepreform stretching apparatus or fibre drawing apparatus are movable, andthe stretching/drawing preferably takes place vertically, particularlyfrom the top downwards, by holding the generated end product in positionrelative to the body of the processing device whereby the gripping meanson the side of the end product remains in position relative to the bodyas the gripping means at the opposite end of the preform and the furnacemove.

The processing apparatus according to the invention can be either anindependent entity intended only for processing a perform or for drawinga fibre from a preform, or it can be an integrated part of the rest ofan apparatus that performs also other actions on the preform or thefibre obtained from it. In addition, the device and the method can beused in shaping a tubular preform to adjust the diameter and to adjustthe wall thickness.

It is obvious to a person skilled in the art that as technologyadvances, the basic idea of the invention can be implemented in avariety of ways. The invention and its embodiments are thus not limitedto the above examples, but may vary within the claims.

1. A device for processing/stretching a preform, the device comprisingat least two gripping means for securing the preform to the processingdevice, at least one heating device for heating the preform or a sectionthereof to a desired temperature, the gripping means and the heatingdevice being arranged movable characterized in that the gripping meansand the heating device are arranged optionally movable so that theyallow the end product produced to be held in position during theprocessing process relative to the body of the processing device,irrespective of the direction of the processing/stretching, by holdingthe gripping means on the side of the end product of the preform inposition relative to the body of the processing device.
 2. A device asclaimed in claim 1, characterized in that the gripping means and theheating device are arranged such that the speed of movement anddirection of movement of each of them are separately adjustable.
 3. Adevice as claimed in claim 1, characterized in that it comprises meansfor rotating the preform around its longitudinal axis during theprocessing.
 4. A device as claimed in claim 1, characterized in that itfurther comprises one or more independently movable cutting device forcutting the preform and/or a fibre.
 5. A method of processing/stretchinga preform comprising the steps of: securing the preform to a processingdevice by means of at least two separate independently movable grippingmeans; heating the preform or a section thereof by means of at least oneindependently movable heating device at least locally; and generating atension in the preform by moving at least one of the gripping means;characterized in that the method further comprises step of: processingthe preform by feeding it to the heating device by moving one of thegripping means and the heating means and by holding the gripping meanson the side of the end product of the preform in position relative tothe body of the processing device whereby the end product produced alsoremains in position relative to the body of the processing device,irrespective of the direction of the processing/stretching.
 6. A methodas claimed in claim 5, characterized in that the speed of movement andthe direction of movement of each gripping means and heating device areseparately adjustable.
 7. A method as claimed in claim 5, characterizedby performing the processing/stretching of the preform vertically fromthe top downwards.
 8. A method as claimed in claim 5, characterized byperforming the processing/stretching of the preform vertically from thebottom upwards.
 9. A method as claimed in claim 5, characterized byrotating the preform around its longitudinal axis during the processing.10. A method as claimed in claim 5, characterized by using two or moreheating devices in the processing of the preform.
 11. A method asclaimed in claim 10, characterized by adjusting the speed and directionof movement of each heating device separately.
 12. A method as claimedin claim 5, characterized by using the method for correcting variationsin the diameter of the preform.
 13. A method as claimed in any claim 5,characterized by using the method for correcting the roundness of thepreform.
 14. A method as claimed in claim 5, characterized by utilizingthe method in association with a sleeving process.
 15. A method asclaimed in claim 5, characterized by utilizing the method in associationwith a collapsing process.
 16. A device for drawing an optical fibrefrom a preform, the device comprising at least two gripping means, ofwhich at least one is provided with coiling means for the optical fibre,for securing the preform to the drawer, and at least one heating devicefor heating the preform or a section thereof to a desired temperature,the gripping means and the heating device being are arranged movablecharacterized in that that gripping means and the heating device arearranged optionally movable such that irrespective of the selecteddrawing direction, the heating device and one of the gripping means aremovable relative to the body of the drawer and to the other grippingmeans, which is immovable relative to the body of the drawer and towhich a coiling device is connected for coiling the end product/opticalfibre to a coil, whereby both a heating device and the gripping meansthat is movable relative to the body of the drawer move relative to thecoiling device that receives the end product/optical fibre.
 17. A deviceas claimed in claim 16, characterized in that the gripping means and theheating devices are arranged such that the speed of movement and thedirection of movement of each of them are separately adjustable.
 18. Adevice as claimed in claim 16, characterized in that it comprisesdevices for rotating the preform around its longitudinal axis during theprocessing.
 19. A device as claimed in claim 16, characterized in thatcoiling means are arranged in each of the gripping means.
 20. A deviceas claimed in claim 16, characterized in that it also comprises one ormore independently movable cutting device for cutting the preform and/orthe fibre.
 21. A method of drawing an optical fibre from a preformcomprising the steps of: securing the preform to a drawer by means of atleast two separate independently movable gripping means; heating thepreform or a section thereof by means of at least one independentlymovable heating device at least locally; generating a tension in thepreform by moving at least one of the gripping means; characterized inthat the method further comprises steps of: drawing optical fibre fromthe preform by moving one of the gripping means and the heating deviceand by holding the gripping means on the side of the produced opticalfibre in position relative to the body of the drawer; and coiling theproduced optical fibre with a coiling device arranged in the grippingmeans that is immobile relative to the body of the drawer onto a coil,whereby both a furnace and the gripping means that is movable relativeto the body of the drawer move relative to the coiling device thatreceives the end product/optical fibre irrespective of the selecteddrawing direction.
 22. A method as claimed in claim 21, characterized inthat the speed of movement and the direction of movement of eachgripping means and heating device are separately adjustable.
 23. Amethod as claimed in claim 21, characterized by performing the drawingof the optical fibre vertically from the top downwards.
 24. A method asclaimed in claim 21, characterized by performing the drawing of theoptical fibre vertically from the bottom upwards.
 25. A method asclaimed in claim 21, characterized by rotating the preform around itslongitudinal axis during the drawings.
 26. A method as claimed in claim21, characterized by using two or more heating devices in the drawing.27. A method as claimed in claim 26, characterized by adjusting thespeed and direction of movement of each heating device separately.
 28. Amethod as claimed in claim 21, characterized by using the method inshaping a tubular preform for both adjusting the diameter and adjustingthe wall thickness.